Electrical transmitting system



I 132,357 March 29, 1 LES ELECTRI CAL TRANSMITTING SYSTEM Filed May 1, 192's 2 sheets-sheet- 1 r I! w m m Q Q I r 1: a

M h 29, 1927- E,,M. STAPLES ELECTRICAL TRANSMITTING SYSTEM Filed May 1. 1925 2 Sheets-Sheet 2' gwat m ATTORNEY Patented Mar. 29, 1927.-

UNITED STATES PATENT oFFlCE.

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ELECTRICAL TRANSMITTI N'G SYSTEM.

Application filed May 1,

other lines when the input electromotive force at the sending end of the system becomes excessive. Another object of my 1nvention is to provide for cutting down the current on the line but keeping the overlo all transmission equivalent unchanged when occasion arises for applying excessive elec- 'tromotive forces at the transmitting end. Still another object of my invention is to provide for cutting down the current on l5 the line in a picture transmitting system when the currents would otherwise become excessive on the line, as when making adjustments etc., and at the same time keeping the transmission equivalent value of the entire system unchanged. These and various other objects of my invention will become apparent on consideration of a limited ,number of specific examples of practice according to the invention, which I have chosen to illustrate and describe in this specification taken with the accompanying drawings. It will be understood that the following description refers to these par ticular examples of theinvention, and that the invention will be defined in the appended claims. "i; 7

Referring to the drawings, Figure 1 is a diagram of the transmitting end of a picture transmitting systemjembodying my invention, Fig. 2 is a diagram of the corresponding receiving end,- and Fig. 3 is a sectional elevation of a modified skeleton transmitting film holder. v

The cylindrical glass drum 14 at the send ing end shown in Fig. '1 has a semi-transparent picture film wrapped about it. This drum is. rotated on its axis .and meanwhile traversed slowly along its axis by 'virtue of the engagement of the screw-threaded shaft 16 with a suitable support. Inside the drum 14 is a photoelectric cell 15, supported op posite the opening in the screen 13. Light from the source 11 is focused by the lens 12 on the spot of the film 14 underlying the opening in the screen 13, and this light passes through the film in degree corresponding to its transparency at the spot involved, and this light entering the photoelectric cell 15 determines the magnitude of 1925. Serial No. 27,253.

the electric current .on the input side of the amplifier A The out at current from the amplifier A of amp ltude determined by the degree of transparenc .of the icture film, goes to the modulator 1 and mo ulates the current from the oscillator 0 The modulated current from M goes through a filter F and through (or past) a network 20, 21, to theamplifier A and the line L. 1

Direct current is applied at 22 to apparatus 23, comprising a periodic interrupter of definite ratefrom which periodic current goes to drive the synchronous motor 17, and also periodic current goes through the filter F to the amplifier A and the line L. F is a high pass filter and F is a low pass filter, and the picture transmitting current and the synchronizing current are respect1vely'of relatively high frequency and low frequency.

Themotor 17 drives the drum 14 through a friction coupling 18, and 19 is a clutch that p locks the "drum 14 against movement except when it is disengaged by energization of the magnet 24. The cam 34 closes the switch 34 just as the space be'tweenthe ends of the film at 35 passes under the opening in they screen 13.-

At the receiving end shown in Fig. 2, the currents coming in on the line L are amplified by amplifier A and separated accordin to their frequency by the high pass filter F and the low pass filter F The high frequency picture transmitting currents /go through (or past) v the network 20'2120 and through the amplifier A to light valve 41.

The low frequency currents through the filter F and amplifier-detector A go to apparatus 23' which is energized from a direct current source connected at 22 and delivers periodic current to the. synchronous motor 17, driving it in step with the motor 17 at the sending end. Themotor 17' drives the drum 14 through a friction coupling 18, and the clutch 19 locks the drum 14 against movement except when released by the energization of the magnet 24.

Light from the source 11 is directed by the lenses 12' through the light valve 41 and the opening in the screen 13' on the underlying spot of a sensitive film wrapped on the drum 14'.

Other structural features of the system their travel, holding open the switches 26 and 26'. Further to prepare for the transmission of the picture as intended, the

operator at the receiving end presses down momentarily on the key42.

At this time the oscillator at the sending end is sending over the line a current of the ure carrier frequency which is receive at the amplifier A and goes to the llght valve 41,

- holdin it at a constant adjustment of openmg. he closure of the key 42 adjusts the amplifier A so that it functions as'a deteotor, and the detected output current acting on the relay 43 closes the contacts 44 and holds the detector adjustment after thekey 42 is released. The energization of the magnet 43 also opens at 45 the circuit of the battery 25 which is also already open at 28'. The receiving operator now throws the switch 28 to the right and his system is ready for the intended operation.

The operator atthe transmitting end, shown in Fig. 1, now throws his switch 28 to the right and then he momentarily presses button 29. This latter operation puts a shunt across the oscillator 0 and interrupts the flow of carrier current over the line to the amplifier A, at the receiving end. Thereupon the relay 43 releases, putting an endto the detector adjustment of the amplifier A so that it thereafter functions as an amplifier, and also closing at 45 the circuit of the battery 25. It results that the magnets 24 and 30 are energized. 24' dis-' engages the clutch 19', permitting the drum 14' to start in motion. The network at'the receiving end, 20'--21'--20 has been cut out until the magnet 30' is energized, and it is then cut intothe circuit.

Simultaneousl at the transmitting end the closure of t e button 29 closes the circuit of the battery 25 on the magnets 24 and 30. The energization of magnet 24 disengages clutch 19, permitting the drum 14 to start in motion. The network 20, 21, 20 has been cut in on the line until the energization of the magnet 30 "cuts it out. The system is now operating normally.

Antecedent to the start-of operation thathas just been described, it is necessary to adjust the apparatus at the transmitting and receiving ends, particularly with reference to getting the right degree of light exposure at the reoeivi end. The.adjustments referred to are ependent in lar' e measure on the character of the film u for transmitting, and hence may need to be made before each transmission. The transmitting currents are attenuated as they go over the line, and the degree of attenuation may varyfrom time to time, as for example in the case of an open wire line the attenuation may be greater in wet weather than in dry weather. These considerations suggest the importance of the preliminary adjustments before the actual picture transmission is started.- v

' In the system as here described transmission is from a positive or negative film at the transmittingend, and the largest currents will be put on the line when the light is the highest in the film, that is, when a spot of relatively high degree of transparency underlies the opening in the screen 13. It will be desirable at such a time to have the intensity of current on the line about as high as will bepermissible without causing inductive interference with other transmission lines in the neighborhood, particularly telephone lines. In making the adjustments referred to before starting the transmission, it might occasionall happen that even stronger currents than t is; permissible maximum would occasionally be put on the 7 line and the networks 20-21-20 at the sendin end and 20'-21'- 20 at the receiving en are arranged to guard against this.

When the drums 14- and 14 at the two ends of the line .reach the respective ends of their travel they open the circuits of batteries 25 and 25 at the switches 26 and .26

at one end of their travel or 27 and 27 at the other end of their travel. It results that the magnets 30 and 30' are deenergized and the network 2021 -20 at the sending end is, cut in and the network 20-21'-20 at the receiving end is cut out. Accordingly,

the over-all transmission equivalent of the system is unchanged, but the currents onthe l ne are materiall reduced in intensity, so that even if in t e process of adjustment the applied electromotive'forces at the'send- 'ing end happen to be unusually large, the

currents on the line are not unusuallydarge as compared with normal transmission.

Of course it is desirable for normal transmission'that the currents on the line shall have considerable intensity so' that they shall not be masked at the receiving end b inter.- ference along the line. Therefore, or normal transmission it becomes desirable. to

change this state of afiairs that has been.

operates to prevent is cut in, so as to bring the transmission level up on the line but keep the over-all transmission equivalent unchanged for the system.

It will be comparatively seldom that the high lights in the picture will give as much as 100% transparency at the corresponding spot of the film on the drum 14. But between the edges of the film at 35 there will be 100% transparency, and hence at this point there would be a pulse of current on the line of maximum intensity. To prevent this I place the cam 34 on the shaft 16 in such position as to close the contacts 34 when the gap between the edges of the film F, so that excessive currents are prevented from going on the line. Ihis short circuit closed at 34:- includes a pair of contacts at 31 which are of course closed by energization of the magnet 30 during picture transmission. However, ,during the preliminary adjustment the short circuit is open at 3l so that if at this time a closure happens to be made at 3% it will be of no efi'ect.

By my invention it becomes practicable to use a telephone'circuit for picture transmis- SlOIl. level for the circuit is determined upon so that there will not be undue interference from the picture transmission circuit to neighboring telephone circuits. Then the result is secured that the currentsare kept well below this level even for the extraordinary conditions, of preliminary adjustment and for the periodically recurrent high light condition due to the spaced edges of the transmitting film on its drum.

In the embodiment of my invention shown in Figs. 1 and 2, transmission is from a positive at the sending end to a negative at the receiving end or from a negative to a positive. High light in the sending film causes large current on the line and this large current causes a wide openin of the light valve at the receiving end and a dark shade in the receiving film.

In Fig. 3 I have shown a skeleton film holder that may be employed instead of the glass drum of Fig. 1 at the transmitting end. The transmitting film has one pair of opposite edges resting on the collars 51 and the other pair of edges meeting along. the bar 52. In this case the system is adjusted so that transmission is from positive to positive or negative to negative and deep shade in the sending film gives large current on the line; hence also the current would be a maximum when the bar 52 intercepts the light to the photoelectric cell, but by my improvement the cam- 34 of Fig. 1.

putting thisplarge .current on the line.

A certain permissible transmission 2. In the operation of a, picture transmitting system the method of protecting neigh boring lines from inductive interference during the period of preliminaryadjustment, which consists in automatically introducing a loss at the sending end and cutting out an equal loss at the receiving end when the apparatus is in the condition preliminary to starting a normal picture transmission.

3. In the operation of a picture transmission system, the method of protecting neighboring lines from inductive interference, which consists in reducing the current on the line when a.regularly recurrent condition in the sending film would otherwise cause a large current to be "applied on the line.

4. In combination, a picture transmitting system comprising at the transmitting end means 'to send currents of intensity corresponding to the degree of light of successive elemental areas of a film, and at the receiving end means to expose a sensitive film to light adjusted -in degree to the intensity of the received currents, and automatic means to introduce loss at the sending end and cut out an equal loss at the receiving end when the apparatus is in the condition preliminary to startingthe normal picture transmission, said means being also operated to out out the said loss atthe' sending end and introduce-it at the receiving end when normal transmission starts.

5. In combination, a transmission line, a loss network normally in the circuit at the receiving end and another loss network normally out at the sending end'and' means to reverse their relation to the circuit While the apparatus is in condition preliminary to normal operation.

6. In a picture transmitting system, the drums 14 and 14, loss networks, one located at each end of the, line, the' one at the sending end being normally out of the line and the one at the receiving end being normally in the line when the drums are at intermediate positions, and means actuated by) the drums at the ends of their ranges of 'travel to reverse the conditions of the re- April 1925.

4 ELLIOT M. STAPLES. 

